1. Field of the Invention
The present invention relates to a sintered polycrystalline diamond composite for use in rock drilling, machining of wear resistant materials, and other operations which require the high abrasion resistance or wear resistance of a diamond surface. Specifically, this invention relates to such bodies that include a polycrystalline diamond layer attached to a cemented carbide substrate via processing at ultrahigh pressures and temperatures.
2. Description of the Art
It is well known in the art to form a polycrystalline diamond cutting element by sintering diamond particles into a compact using a high pressure, high temperature (HPHT) press and a suitable catalyst sintering aid. Apparatus and techniques to accomplish the necessary sintering of the diamond particles are disclosed in U.S. Pat. No. 2,941,248 to Hall and U.S. Pat. No. 3,141,746 to DeLai.
U.S. Pat. No. 3,745,623 Wentorf et al. teaches sintering of the diamond mass in conjunction with tungsten carbide to produce a composite compact (PDC) in which the diamond particles are bonded directly to each other and to a cemented carbide substrate.
It has been proven challenging to produce a PDC with an average grain size of diamond less than about 1 micron. This sub-micron diamond powder is difficult to produce and handle during the processes involved in sintering a uniform diamond body and attaching it to a substrate. Additionally the property of this material to agglomerate and its low packing density produces a diamond compact containing re-precipitated diamond crystals that results in lowering the strength of the overall structure.
Attempts to overcome the difficulties in sintering sub-micron diamond have been proposed by Hara et al. in U.S. Pat. No. 4,303,442. These solutions, however, do not provide a PDC with enough uniformity in abrasion and impact resistance to be useful in drill bits for deep hole oil and gas drilling.
It is well known in the art to mix a catalyst with the diamond prior to HPHT sintering in order to provide a uniform mixture of these materials. This is especially helpful when working with very fine grain diamond that is difficult to penetrate with a catalyst when the fine grain diamond is densely compacted. A problem still exists after the catalyst melts since it dissolves the fine diamond grains which re-precipitate as larger diamond crystals in a non-uniform distribution throughout the sintered mass. U.S. Patent Application No. 20090178345 to Russell et al attempts to solve this problem by milling the diamond with a catalyst that itself has a very fine grain size. Unfortunately these finer size catalyst particles combine after melting and create the same problems of dissolving the very fine diamond crystals.
Thus, there remains a need to effectively control the grain size of very fine diamond used in the formation of polycrystalline diamond cutting tools.